This invention relates to yarn containing polyester fibers having an improved balance of properties including tenacity and boiling water shrinkage, which find particular application in textile uses.
Polyester fibers have been prepared for commercial use for more than thirty years, and are produced in large quantities. Most commercial polyester comprises linear terephthalate polyesters.
The term "fiber" as used herein includes fibers of extreme or indefinite length (i.e., filaments) and fibers of short length (i.e., staple). The term "yarn", as used herein, means a continuous strand of fibers.
Because fibers produced from polyester have a number of outstanding characteristics including excellent dimensional stability and sturdiness, a high degree of crease resistance, good bulk elasticity, and warm handle, the fibers have found a wide variety of applications, especially in the textile field.
Many textile applications require yarns containing polyester fibers having predetermined limits with respect to tenacity and boiling water shrinkage. Some procedures utilized to produce polyester fibers result in fibers having an acceptable (low) boiling water shrinkage, but a tenacity which is too low. Conversely, other procedures utilized to produce polyester fibers result in fibers having an acceptable tenacity, but an unacceptable boiling water shrinkage Even within the acceptable tenacity and boiling water shrinkage limitations, certain variations in boiling water shrinkage and tenacity of the fibers are required for certain textile applications. Still further, some processing applications require that the fibers have sufficient elongation so that they can be further processed.
For instance, it is sometimes desirable to produce fibers which have a lower tenacity which, during further processing, can be broken in order to provide a yarn containing polyester fibers having a "good feel". Furthermore, in many textile applications where high tenacity fibers are not of critical importance, a low boiling water shrinkage is sometimes desired.
Thus, a need exists for a process which facilitates the uniform preparation of a yarn comprising polyester fibers within predetermined limits of fiber properties including tenacity and boiling water shrinkage.